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From: Eric Dumazet <edumazet@google.com>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Dmitry Vyukov <dvyukov@google.com>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	David Miller <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	syzbot <syzkaller@googlegroups.com>
Subject: Re: [PATCH] inet: frags: Remove unnecessary smp_store_release/READ_ONCE
Date: Fri, 31 May 2019 10:11:32 -0700	[thread overview]
Message-ID: <CANn89iLJAM8kB8ySk2hDReewbL3AqrcEZb8Zf64=mj-cda=onA@mail.gmail.com> (raw)
In-Reply-To: <20190531162945.GA600@andrea>

On Fri, May 31, 2019 at 9:29 AM Andrea Parri
<andrea.parri@amarulasolutions.com> wrote:
>
> On Fri, May 31, 2019 at 08:45:47AM -0700, Eric Dumazet wrote:
> > On 5/31/19 7:45 AM, Herbert Xu wrote:
>
> > > In this case the code doesn't need them because an implicit
> > > barrier() (which is *stronger* than READ_ONCE/WRITE_ONCE) already
> > > exists in both places.
>
>
> > I have already explained that the READ_ONCE() was a leftover of the first version
> > of the patch, that I refined later, adding correct (and slightly more complex) RCU
> > barriers and rules.
>
> AFAICT, neither barrier() nor RCU synchronization can be used as
> a replacement for {READ,WRITE}_ONCE() here (and in tons of other
> different situations).  IOW, you might want to try harder.  ;-)

At least the writer side is using queue_rcu_work() which implies many
full memory barriers,
it is not equivalent to a compiler barrier() :/

David, Herbert, I really do not care, I want to move on fixing real
bugs, not arguing with memory barriers experts.

Lets add back the READ_ONCE() and be happy.

  reply	other threads:[~2019-05-31 17:11 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-24 16:03 [PATCH net-next 00/11] inet: frags: avoid possible races at netns dismantle Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 01/11] inet: rename netns_frags to fqdir Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 02/11] net: rename inet_frags_exit_net() to fqdir_exit() Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 03/11] net: rename struct fqdir fields Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 04/11] ipv4: no longer reference init_net in ip4_frags_ns_ctl_table[] Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 05/11] ipv6: no longer reference init_net in ip6_frags_ns_ctl_table[] Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 06/11] netfilter: ipv6: nf_defrag: no longer reference init_net in nf_ct_frag6_sysctl_table Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 07/11] ieee820154: 6lowpan: no longer reference init_net in lowpan_frags_ns_ctl_table Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 08/11] net: rename inet_frags_init_net() to fdir_init() Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 09/11] net: add a net pointer to struct fqdir Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 10/11] net: dynamically allocate fqdir structures Eric Dumazet
2019-05-24 16:03 ` [PATCH net-next 11/11] inet: frags: rework rhashtable dismantle Eric Dumazet
2019-05-28  6:34   ` Herbert Xu
2019-05-28 13:31     ` Eric Dumazet
2019-05-29  5:40       ` [PATCH] inet: frags: Remove unnecessary smp_store_release/READ_ONCE Herbert Xu
2019-05-29  5:43         ` Dmitry Vyukov
2019-05-29  5:47           ` Herbert Xu
2019-05-31  8:24             ` Dmitry Vyukov
2019-05-31 14:45               ` Herbert Xu
2019-05-31 15:45                 ` Eric Dumazet
2019-05-31 16:29                   ` Andrea Parri
2019-05-31 17:11                     ` Eric Dumazet [this message]
2019-06-07 12:06                       ` Dmitry Vyukov
2019-05-31 17:11                   ` Paul E. McKenney
2019-05-31 17:18                     ` Eric Dumazet
2019-05-29 21:30         ` Eric Dumazet
2019-05-30 18:51         ` David Miller
2019-05-26 21:26 ` [PATCH net-next 00/11] inet: frags: avoid possible races at netns dismantle David Miller

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